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chapter 16 cell bio
Terms in this set (72)
a mutation in the bacterial gene encoding crescentin would likely have an effect on which type of bacteria?
curved or spiral shaped
the basic structural polysaccharide of fungal cell walls, crab shells, and insect exoskeletons is
cellulose, chitin, and hyaluronan are al deposited extracellularly by
plasma membrane enzyme complexes
animal cells are embedded in an
why are collagen fibrils formed extracellularly even though their components are synthesized within the cell and transported to the cell surface via the Golgi?
type 1 procallagen is synthesized with non helical segments at each end of the polypeptide chain, limiting their ability to form collagen fibrils in the cells
fibrous structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called
the major function of adhesion proteins like fibronectin is to
link collagen, proteoglycans, and cells containing integrins
Integrins link extracellular matrix proteins either directly or indirectly to all of the following intracellular proteins except
the cell-cell interactions mediated by the selectins, integrins, and most members of the Ig superfamily are blank interactions which the cytoskeleton of adjacent cells are not linked to one another
Homophilic interactions between cells involve interactions
among adhesion molecules of the same molecular class
adherens junctions and desmosomes may be distinguished from each other on the basis of
adherens junctions linkage is with actin filaments while desmosomes link to intermediate filaments
specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cell-surface glycoproteins called
a major function of tight junctions is to
seal the space between adjacent cells to provide a barrier to block diffusion across epithelial cell layer or block diffusion between apical and basolateral surfaces of cells
junctions between animal cells that allow free passage of molecules smaller than about 1000 daltons are called
what is thought to be the functional equivalent of gap junctions in plants?
what does the cell wall do?
determines cell shape and prevents cells from swelling and bursting due to osmotic pressure
what are the different shapes of bacterial cell walls?
-round - coccus
-rod - bacillus
-spiral - spirillium
what is the principal component of bacterial cell walls?
peptidoglycan which forms a strong covalent shell around the entire cell
how does bacterial cell wall synthesis work?
-regulated by cytoskeletal proteins
-FtsZ is a cytoskeletal protein that that forms a ring structure at the site where cell division occurs directing synthesis of the new cell wall that separates the newly formed daughter cells
what is MreB?
a cytoskeletal protein for rod shaped bacteria that directs cell wall synthesis during cell elongation
what proteins do spiral shaped bacteria contain?
intermediate filament related proteins that are responsible for curvature of the cell wall
eukaryotic cell walls are found in and composed of?
-algae, fungi, and higher plants
what is chitin?
-structural polysaccharide of fungal cell walls which forms the shells of crabs and exoskeletons
-linear polymer of N-acetylglucosamine
what is cellulose?
-what the cell walls of most algae and higher plants are composed of
-linear polymer of glucose
-36 cellulose chains join to form microfibrils
plant cell wall characteristics
-cellulose microfibrils and hemicelluloses are embedded in a gel like matrix formed by pectins
-hemicelluloses are hydrogen bonded to cellulose microfibrils and used for stability and mechanical strength
primary cell walls
-thin and flexible
-going through a lot of growth
-equal amounts of pectin, cellulose, and hemicellulose
what do pectins do?
bc they have multiple negative charges, they bind positively charged ions and trap water molecules to form gels
secondary cell walls
-in b/t primary cell wall and plasma membrane
-happens after cell growth has stopped
-usually no pectin, mostly cellulose
-presence of lignin
what is lignin?
-its found in the woody parts of a plant
-gives it strength and density
what is turgor pressure?
-an internal hydrostatic pressure that stops water from moving into the cell eventually equalizing the osmotic balance
-responsible for much of the rigidity of plant tissues
plant cells can expand by taking u water without making new cytoplasmic components through what?
what are auxins?
-a plant hormone that activates expansins
-expansins act to weaken regions of the cell wall allowing turgor pressur to drive expansion of the cell in that direction
-water that flows into the cell accumulate in a large vacuole so the cell expands without increasing the volume of its cytosol
what is cellulose synthase?
transmembrane enzyme that synthesis cellulose from UDP-glucose in the cytosol
cellulose synthase during cell elongation:
UDP glucose binds to cellulose synthase in the cytosol and the growing cellulose chain is translocated to the outside of the cell
what do the cortical microtubules do?
define the direction of cell wall growth which determines the direction of cell expansion and the shape of the entire plant
what are CLASP proteins?
they prevent destabilization and bind to the plus ends of microtubules
what is the extracellular matrix?
-what most animal cells are embedded into
-fills the spaces between cells, helps establish organization, and binds cells and tissues together
-most abundant in connective tissue
what is the basal laminae?
-thin layer of extracellular matrix that support epithelial cells
-surrounds muscle cells, adipose cells, and peripheral cells
what is the extracellular matrix composed of?
-tough fibrous proteins embedded in gel like polysaccharides
what are adhesion proteins?
link components of the matrix both to one another and to attached cells
Lots of fibrous proteins to make them strong and solid to keep those connections
fibrous proteins and high levels of polysaccharides so there is more flexibility, cushioning for stress, and to make sure bones aren't hitting each other
Has calcium phosphate crystals which gives it density and strength to use for leverage for movement
What is the major structural protein of the extracellular matrix?
-three polypeptide chains coil around one another to form a triple helix structure
-consists of repeats of the amino acid sequence Gly-X-Y
-most abundant collagen
-assemble in collagen fibrils outside the cell
-don't form within cell bc they are synthesized as procollagens that have non helical segments at both ends of polypeptide chain
type 1 collagen
-basal laminae forms from this
-network forming collagen
-Gly-X-Y repeats are interrupted by short non helical sequences
-assembles in 2D cross linked networks
type IV collagen
What is elastin?
-what makes up elastic fibers
-cross linked into a network by covalent bonds formed b/t the side chains of lysine residues
-stretches under tension and snapping back when tension is released
What are glucosaminoglycans (GAGs)?
-repeating units disaccharides
-highly negatively charged
-they bind + charged ions and trap water molecules to form hydrated gels to provide mechanical support to extracellular matrix
What is hyaluronan?
-the only GAG that occurs as a single long polysaccharide chain
-synthesized at the plasma membrane by hyaluronan synthase
What are proteoglycans?
-a protein linked with glycosaminoglycans
-can contain 1-100+ GAG chains
-interact with hyluronan to form large complexes
-main adhesion protein of connective tissue
-has two polypeptide chains
-cross linked into fibrils
-has binding sites for both collagen and proteoglycans
-cells can bind via integrins
-major organizers of basal lamina assembly
-consist of 3 polypeptide chains
-subunits have binding sites for cell surface receptors (integrins) and proteoglycans
-responsible for the attachment of cells to the extracellular matrix
-consists of two subunits alpha and beta
-bind to various components of extracellular matrix
-serve as anchors for cytoskeleton
interactions between integrins and the cytoskeleton are found at two types of cell matrix junctions which are?
focal adhesions and hemidesmosomes
-cytoplasmic domains of the beta subunits of integrins anchor the actin cytoskeleton by associating with bundles of actin filaments
-develop from small integrins called focal complexes
-mediates epithelial cell attachments at which a specific integrin (designated a6B4) is linked to intermediate filaments
-anchors intermediate filaments in a cell to the basal lamina
-used to modify extracellular matrix
-digest variety of matrix proteins
-play roles in cell movement during development
cell-cell interactions are critical for
-development and function of multicellular organisms
-some interactions are transient and others are stable
-selective process that cells adhere to other cells of specific types
-mediated by cell adhesion molecules
-mediate transient interactions between leukocytes and endothelial cells or blood platelets
-recognize cell surface carbohydrates
two different molecules interacting with each other
two of the same molecules interacting
-region of cell-cell adhesion at which the actin cytoskeleton is anchored to the plasma membrane
-cadherins link the actin filaments (cytoskeleton) of one cell to the actin filaments of another
desmosomal cadherins (desmoglein and desmocollin) link intermediate filament cytoskeletons of adjacent cells
what are tight junctions?
-separate apical and basolateral domains by preventing the free diffusion of lipids and membrane proteins b/t them
-form seals that prevent the free passage of molecules and ions b/t cells
how are tight junctions formed?
-a network of protein strands that continues around the entire cell
-each strand is composed of transmembrane proteins
-the cytosolic tails of the transmembrane proteins link the tight junction complex to the actin cytoskeleton
what is the middle lamella?
-acts as a glue to hold adjacent cells together
-only seen b/t cells that have replicated and divided
what are gap junctions?
-provide direct connections b/t cytoplasms of adjacent cells
-regulated channels through the plasma membrane
-allow ions and small molecules to diffuse freely when open
-most cells in animals communicate by gap junctions
what are gap junctions constructed of?
transmembrane proteins of the connexin family
how many connexins form a connexon?
what is the function of plasmodesmata?
-functions analogously to gap junctions as a means of direct communication b/t adjacent cells
-important role in signaling in plants by allowing regulatory molecules to travel directly b/t cells
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